1. Field of the Invention
The present invention relates to a diagnosis device for determining whether or not an internal combustion engine exhaust gas recycling device used in a vehicle such as an automobile is functioning correctly.
2. Description of the Prior Art
Generally an exhaust gas recycling device to be incorporated in an internal combustion engine used in a vehicle such as an automobile incorporates an exhaust gas recycling control valve for controlling the recycling flow rate of the exhaust gas, a vacuum control valve for controlling the background pressure, a temperature sensing valve, and so forth, and if there is a fault in any of these structural components, the exhaust gas recycling will no longer be carried out and there is a danger of the internal combustion engine being operated in a state where the reduction in NOx in the exhaust gas is not carried out. Even if the exhaust gas recycling is not carried out because of a failure, the internal combustion engine will still operate without failing, and may therefore be driven for a long time without the driver realizing; this gives rise to atmospheric pollution problems.
In view of the above situation, a failure alarm device has already been proposed constructed such that when the exhaust gas recycling has stopped because of a failure of the exhaust gas recycling device the user is informed and given an opportunity for repair, and this is disclosed in for example Japanese Utility Model Publication Sho No. 52-9471 (1977) and in Japanese Utility Model Laying Open Publication Sho No. 62-71363 (1987).
Fault diagnosis of the exhaust gas recycling device may be carried out basically by, under conditions such that exhaust gas recycling should be carried out, determining whether or not, for example, the temperature within an exhaust gas recycling passage is at least a certain value, in other words by determining that when said temperature is not more than a certain value exhaust gas is not flowing in the exhaust gas recycling passage, and thus determining that the exhaust gas recycling device has failed, but the actual temperature of said exhaust gas recycling passage is altered by the repeated carrying out and stopping of exhaust gas recycling and therefore it is difficult to determine definitively whether or not exhaust gas is flowing through the exhaust gas recycling passage simply by the level of this temperature, and there is the problem that if diagnosis of the exhaust gas recycling device is carried out by simply determining the temperature of the exhaust gas recycling passage under conditions in which exhaust gas recycling is being carried out, then the diagnosis may not necessarily be correct.
The present invention has as its object the provision of an improved exhaust gas recycling device diagnosis device which solves the above problems.